The present invention relates to a semiconductor device of what is called a chip on chip (hereinafter, abbreviated as COC) type semiconductor device, in which a plurality of semiconductor chips are electrically connected so that they face each other and a method for manufacturing the same. More particularly, the invention relates to a semiconductor device using multiple chips, in which a plurality of second semiconductor chips are directly connected on the surface of a first semiconductor chip while an interconnection for connecting the second semiconductor chips can be freely changed without depending on internal design of the first semiconductor chip.
Conventionally, in the case of constructing a semiconductor device by combining circuits such as a memory device and its logic circuit, for reduction in an area occupied by forming the circuits three-dimensionally, reduction in parasitic capacity of an RF circuit or the like, generalization of a part of a circuit (for example, a memory device portion is generalized and a driving circuit portion is changed according to an application), and a case where the circuits cannot be formed on one chip due to different fabrication parameters of the circuits, a semiconductor device of the COC type having the structure that a semiconductor circuit is fabricated by a plurality of chips and a semiconductor chip (child chip) is connected onto another semiconductor chip (parent chip) may be used. In recent years, there is a tendency that a multi-chip device in which a plurality of child chips are provided as shown in FIG. 12 is used.
In FIG. 12, electrode terminals 22 of second semiconductor chips (child chips) 2a and 2b are connected onto electrode terminals 12 on a first semiconductor chip (parent chip) 1 via bump electrodes 11 and 21, respectively. The parent chip 1 is bonded to an island (not shown) constructed by a lead frame. Electrode pads (not shown) provided on the peripheral side of the parent chip 1 are electrically connected to leads (not shown) provided around the island via wires such as metal wires, and the periphery is molded by a resin (not shown). Reference numeral 17 denotes a passivation film.
As described above, in the semiconductor device of the COC type, the parent chip 1 and child chips 2a, 2b are connected to each other via the bump electrodes 11 and 21 or the like provided on the electrode terminals. The semiconductor device is connected to external leads via the wires and the electrode pads provided around the parent chip 1. Signals are therefore transmitted between the parent chip 1 and the child chips 2 via bump electrodes. However, in the case where signals are transmitted between the plurality of child chips 2a and 2b, an interconnection is formed in a semiconductor layer or in an insulating film in the surface of the semiconductor layer of the parent chip 1, and end parts of the interconnection are exposed as electrode terminals from the insulating film and connected to the electrode terminals of the child chips.
As described above, in the case of transmitting signals between the parent chip and the child chip in the semiconductor device of the COC type, it is sufficient to connect the electrode pads of the parent chip and the child chip via the bump electrodes. However, in the case where signals are transmitted among a plurality of child chips, signals have to be transmitted via the interconnection formed in the parent chip. Even in the case where the parent chip or the like is generalized and a circuit according to an application is formed by child chips, an interconnection has to be formed in the parent chip in accordance with the child chips to be mounted. There is consequently a problem such that generalization of the parent chip is limited.
Further, in the case where signals have to be transmitted from the outside to one of child chips, signals have to be transmitted to the child chip via the electrode pad and the interconnection in the parent chip. It hinders the generalization of the parent chip.
Further, since the parent chip and child chips are connected via bump electrodes made of Au or the like, if the connecting work is not performed at a high temperature such as 450xc2x0 C., excellent electric connection cannot be obtained. In this case, however, the semiconductor substrate is also heated to the high temperature and pressure applied on the bump electrodes is also applied on the semiconductor substrate, so that circuit elements cannot be formed under the bump electrodes on both of the chips. It causes a problem that the efficiency of using the semiconductor substrate deteriorates.
The present invention has been achieved in consideration of such circumstances and an object thereof is to provide a semiconductor device of a COC type in which, while obtaining generalization of a first semiconductor chip, a signal can be transmitted/received between second semiconductor chips formed on the first semiconductor chip without changing design in the first semiconductor chip of the semiconductor device and a method for manufacturing the semiconductor device.
Another object of the present invention is to provide a semiconductor device in which a signal can be transmitted from the outside directly to a child chip connected on a parent chip via an electrode pad of the parent chip while using the generalized parent chip without forming a special interconnection in a semiconductor layer or an insulating layer of the parent chip.
Further another object of the present invention is to provide a semiconductor device having sufficiently increased packing density by making it possible to form circuit elements also in a semiconductor layer under electrode terminals by preventing a high pressure from being applied on a bump electrode at high temperature at the time of connecting a parent chip and a child chip.
Further another object of the present invention is to provide a semiconductor device having improved packing density by making it possible to form a device also under an electrode pad by preventing excessive increase in temperature and application of a pressure with an ultrasonic wave or the like when a wire such as a metal wire for performing wire bonding and an electrode pad are bonded to each other.
According to the present invention, there is provided a semiconductor device in which a plurality of second semiconductor chips are connected to the surface side of a first semiconductor chip via electrode terminals provided on each of the first semiconductor chip and the second semiconductor chip, wherein an interconnection for directly connecting electrode terminals of two second semiconductor chips out of the plurality of second semiconductor chips is formed on the surface of a passivation film of the first semiconductor chip. The semiconductor chip includes not only a semiconductor integrated circuit (IC) but also a discrete part such as a transistor, diode, or capacitor. The substrate is not limited to a silicon substrate or a semiconductor substrate of GaAs or the like, but other substrates on which electronic parts are formed can be also used.
With the structure, since the interconnection is formed on the surface of the passivation film, even when the connection between the second semiconductor chips mounted on the larger first semiconductor chip varies, it is unnecessary to fabricate the semiconductor device by changing the design of the first semiconductor chip. At the time of forming a bump electrode or a metal film which can be bonded to the bump electrode of the second semiconductor chip on the electrode terminal on the surface, the interconnection for connecting necessary electrode terminals can be formed by using the material of the bump electrode or the metal film, and desired connection can be made. Consequently, even in the case of changing the second semiconductor chip or the structure of connection between the second semiconductor chips, a generalized chip as the first semiconductor chip can be used without changing the design of the first semiconductor chip. Thus, very high flexibility is achieved.
Concretely, two electrode terminals are formed on the first semiconductor chip in a portion corresponding to each of the electrode terminals of the two second semiconductor chips directly connected to each other, and an electrode terminal of the first semiconductor chip and an electrode terminal of each of the two second semiconductor chips are electrically connected to each other via at least one bump electrode. In the structure, the interconnection is formed simultaneously with the bump electrodes formed on the two electrode terminals of the first semiconductor chip.
Alternately, the at least one bump electrode may be formed on each of the electrode terminals of the two second semiconductor chips, and the interconnection is formed on the first semiconductor chip between the two electrode terminals by using a material which can be bonded to the at least one bump electrode of the second semiconductor chip.
The material which can be bonded means a material which can be easily bonded to a bump electrode at a low temperature such as the material same as that of the bump electrode of the second semiconductor chip or the material which is easily alloyed with the material of the bump like Cu to soldering. It is preferable that the bump electrode has at least an Au layer since the reliability with respect to temperature, moisture, and the like is high.
According to another aspect of the present invention, there is provided a semiconductor device in which a second semiconductor chip is connected to the surface side of a first semiconductor chip via electrode terminals provided on each of the first semiconductor chip and the second semiconductor chip, having the structure that one electrode terminal is formed on the first semiconductor chip in a portion corresponding to any of electrode terminals of the second semiconductor chips, the one electrode terminal and an electrode pad for connection to an external lead provided on the outside of the first semiconductor chip are connected to each other via an interconnection formed on the surface of a passivation film, and an electric signal can be transmitted directly to the second semiconductor chip via the electrode pad of the first semiconductor chip.
With the structure, it is unnecessary to pre-form a special interconnection in the first semiconductor chip as a parent chip, so that generalized chip can be obtained. A signal can be transmitted to the second semiconductor chip as a child chip from an external lead via the electrode pad of the parent chip (first semiconductor chip).
By connecting the electrode terminal of the first semiconductor chip and that of the second semiconductor chip to each other via an Auxe2x80x94Sn alloy layer, the alloy layer is alloyed and fused at a low temperature of approximately 300xc2x0 C. or lower. It is unnecessary to increase the temperature to a high temperature at which an influence is exerted on circuit elements. So the circuit elements can be formed also in a semiconductor layer under the electrode terminals. Thus, the circuit elements can be formed with very high density.
According to further another aspect of the present invention, there is provided a semiconductor device including: a semiconductor substrate in which a circuit element is formed; an electrode pad for wire bonding provided either on the surface of the semiconductor substrate via an insulating film or in contact with the semiconductor substrate; and a wire to be bonded to the electrode pad so as to be connected to an external lead, wherein an Au layer and an Sn layer or an Auxe2x80x94Sn layer are provided on the surface of the electrode pad, and the wire and the electrode pad are connected to each other via an Auxe2x80x94Sn alloy layer.
With the structure, at the time of performing wire bonding, it is unnecessary to rub the bonding pad portion with an ultrasonic wave, and the connecting work can be made while hardly applying a pressure. Consequently, even when a device such as a transistor is formed in a semiconductor layer under an electrode pad to which a wire is bonded, a problem such that the device is damaged during bonding does not occur. As a result, a number of devices can be formed in a single semiconductor chip, and the packing density can be improved.
According to further another aspect of the present invention, there is provided a semiconductor device including: a first semiconductor chip having a first bump electrode; a second semiconductor chip including a second bump electrode having a top surface area smaller than that of the first bump electrode; and an Auxe2x80x94Sn alloy layer for bonding the second bump electrode onto the first bump electrode, wherein a step by which at least a part of the peripheral portion of the first bump electrode becomes lower than a center portion side is formed, and wherein a fillet of the Auxe2x80x94Sn alloy layer is formed so as to extend from a top face on the center portion side of the first bump electrode to the periphery of the second bump electrode.
According to the present invention, there is also provided a method for manufacturing a semiconductor device in which each of one or a plurality of second semiconductor chips is connected to the surface side of a first semiconductor chip via electrode terminals, comprising the steps of: forming two electrode terminals or one electrode terminal in a portion of the first semiconductor chip in correspondence with the electrode terminals of two second semiconductor chips out of the plurality of second semiconductor chips or the electrode terminal of the second semiconductor chip to be connected to an electrode pad for connection to an external lead provided on the first semiconductor chip; forming a bump electrode on each of the one or two electrode terminals of the first semiconductor chip and simultaneously forming an interconnection for electrically connecting between the two electrode terminals or between the one electrode terminal and the electrode pad; and connecting the first and second semiconductor chips via the bump electrode, thereby electrically connecting the electrode terminals of the two second semiconductor chips or the electrode terminal of the second semiconductor chip and the electrode pad via the interconnection.
The bump electrode and the interconnection can be formed by, for example, forming a barrier layer in a desired pattern by a film forming method such as sputtering, vacuum deposition, laser abrasion, or CVD, and after that, by performing electrolytic plating or the like.
Alternately, in place of forming the bump electrode on each of the one or two electrode terminals of the first semiconductor chip, forming a bump electrode which is formed on each of the electrode terminals of the one or two second semiconductor chips, and forming an interconnection for connecting between the two electrode terminals or between the one electrode and the electrode pad of the first semiconductor chip by using a material which can be bonded to the bump electrode. In this case, by continuously forming the barrier layer and a film made of the material which can be bonded to the bump electrode, a desired pattern can be formed.